I was hired by a member of a non-profit organization and during the contract process, I wasn't too sure if he should sign with his name or use his organization's name? I had him use the organization's name. What about the invoice? Whose name should be on it? Any one can maybe show some examples of their invoices?

e.g. Employer is John Smith. The non-profit organization he's in is Pet Coalition.

Whoever you are signing the contract with should have their name on the contact and invoice. If you are doing business with a business, then someone should sign as an office/owner/member/representative of that business and that name should be on the invoices, too. If the business is actually an individual or you don't trust the business to be creditworthy then you can make the contact with an individual, but usually that's not the case.

When you are selling your products and services to a company, you probably want to enter into a contract with the company itself.

The problem here is: does John Smith have the right to act on behalf of the Pet Coalition? In the US, it is usually a requirement to get a corporate resolution {a document that indicates the name and title of the corporate officers that can sign on behalf of the company} if you want to enter into some types of transactions such as opening checking accounts, borrowing or selling real estate.

The whole idea behind it is to make sure that only a select group of employees can get the corporation into contracts. Otherwise, the janitor for McDonald’s could sign a contract on behalf of McDonald’s.

If Per Coalition is a small non-profit organization, and John Smith is listed as one of the officers in the State where it was created {records are usually public and accessible through the internet}, I would feel comfortable that he is allowed to sign on behalf of the company.

It is good to note that in case of non-compliance your recourse would be against Pet Coalition not John Smith.

Disclaimer: I am not an attorney, and the above is just how I would approach it.

Edit: I read your original post again and this John Smith lists himself as a "special advisor", this probably means that he is not an official part of the non-profit. If he is not part of the non-profit's board or an officer of the non-profit.... then he most likely does not have the authority to enter into a contract on their behalf {unless he himself has a contract that allows him to do so}. Might want to get the contract confirmed by an officer / board member of the non-profit.

He is either authorized to sign contracts for the business or not. Usually this means he's a director or principal, etc.

There is more to a contract than just the signature on the line. Are you concerned that about whether the agreement is binding? If 'everyone agreed to hire me' then you may not need to worry about who signed it.